1. Field of the Invention
The present invention relates to a hand lever device. In particular, the hand lever device is preferably mounted on a working machine, such as a hedge trimmer or brush cutter, in the vicinity of a hand grip so that it is easy and convenient to operate a driven member such as a throttle valve of an internal combustion engine via a cable.
2. Description of the Related Art
In general, in a conventional working machine, such as a hedge trimmer and brush cutter, which comprises an operative portion including a cutting blade or the like driven by an internal combustion engine, a hand lever device is provided for controlling the degree of opening of a throttle valve of the internal combustion engine. Such a hand lever is mounted in the vicinity of a grip of a U-shaped handle, a bar handle, or the like of the working machine to provide manual control of the throttle valve of the internal combustion engine or the like.
The hand lever device is generally provided with a throttle lever operated by operator's fingers with the throttle lever being pivotally operated to thereby control the degree of opening of the throttle valve via a throttle cable. In general, the throttle valve is always biased toward the direction of minimum valve opening that allows the engine to idle. Accordingly, the throttle valve is normally kept at the idle opening position and, when the throttle cable is drawn in a predetermined amount to eliminate play, it begins to open from the opening position for idling (slow running) of the engine toward an opening position for operation (higher speed running) of the engine.
Examples of such known hand lever devices for controlling throttle valve settings include a type wherein when such a throttle lever is released from a pivotally operated position, the lever is automatically returned to its original idle position setting, thereby automatically moving the throttle valve to its idle setting; and a type where, even if fingers are released from a throttle lever, the throttle lever is held at a desired pivotally operated position.
In both types, when the throttle lever which has once been released to suspend operation is returned to the previous opening degree to resume operation, the pivotally operated position of the throttle lever must be readjusted. In view of such cumbersome operation, there are problems in operability.
To solve the above problems, a hand lever in which the throttle valve can be adjusted appropriately in its opening degree via a cable, kept at a desired opening degree, and yet immediately returned to the minimum opening degree (the opening degree for idle running), and the throttle valve can be brought to the opening degree at which it had stood before it was returned to the minimum opening degree without necessity of readjustment is proposed in Japanese Patent Application No.108340/1995.
The proposed hand lever device comprises a main lever and a sub-lever which are pivotally operated. The sub-lever is adapted to draw a cable connected to a throttle valve via a pulley, and the main lever acts as a link of a toggle mechanism. By pivotally operating the main lever, the pulley is moved which is pivotally held by a slider of the toggle mechanism.
In the hand lever device constructed as described above, when the main lever is operated to pivot to a position close to a grip of a handle, the throttle cable is drawn via the pulley in a predetermined amount to eliminate play, thereby bringing the throttle valve to the minimum opening degree (the opening degree for idle running). Then, the sub-lever is pivotally operated with the main lever held at the above-mentioned position. The throttle cable is thereby further drawn via the pulley. This means that the throttle valve is adjusted in its opening degree from the minimum opening degree to a intended opening degree. By the adjustment of the opening degree, an internal combustion engine is actuated at a desired rotational speed.
In this condition, even if the operator's hold on the sub-lever is released, the sub-lever is kept at the pivotally operated position by frictional force or the like, and the throttle valve is thus kept at the adjusted opening degree.
When the main lever is released from the above condition, the throttle cable is returned to the non-operating position to return the throttle valve to the opening degree for idle rotation because the throttle cable is biased toward the throttle valve closing direction. As a result the engine idles.
In the proposed hand lever device, the toggle mechanism is used to relieve stress exerted on the fingers when the main lever is at the set position close to the grip of the handle, and the pulley is used to magnify the amount of movement of the throttle cable. However, the hand lever device constructed as described above is rather large in size as a whole, and accordingly, the demand for size reduction is not yet sufficiently satisfied. Further, it has a room for improvement in assembling properties.
Moreover, the amount of movement of the throttle cable is magnified by the use of the pulley. However, the amount of pivotal movement of the main lever is still large. Accordingly, there is a problem in operability of the lever and there is still room for improvement in operability.
Furthermore, the sub-lever is kept at its pivotally operated position by frictional force or the like. However, frictional force has problems in that the position tends to be accidentally shifted, and that the pivotally operated position cannot be determined precisely.